Correction for spatio-temporal aberrations.
(a) The spatially resolved second order autocorrelation function of one of the nondiffracting sub-beams (“needle beams”) of the Shack-Hartmann sensor under strong off-axis conditions (angle of incidence about 43°) reveals significant spatio-temporal coupling effects corrupting the pulse quality. The resulting pulse duration was by about 450 attoseconds longer compared to the corrected case (10 fs FWHM of the autocorrelation function, with dispersion compensation) shown in (b). Here, the programmed axicon shape was adapted to the off-axis geometry. For noise reduction and compensation of slight intensity fluctuations at certain time intervals, the experimental data was low-pass filtered.